http2: switch to new runtime-controlled debugging system

Remove `--debug-http2` as a compile-time feature and
make all debug statements available using `NODE_DEBUG_NATIVE=http2`
at runtime.

This probably makes the debugging-enabled case a bit slower due to
additional string concatenations, but switching to a runtime-checking
system makes debugging more flexible and can be applied more easily
to other parts of the source code as well.

configure

@@ -443,11 +443,6 @@ parser.add_option('--debug-lib',
     dest='node_debug_lib',
     help='build lib with DCHECK macros')
 
-http2_optgroup.add_option('--debug-http2',
-    action='store_true',
-    dest='debug_http2',
-    help='build with http2 debug statements on (default is false)')
-
 http2_optgroup.add_option('--debug-nghttp2',
     action='store_true',
     dest='debug_nghttp2',
@@ -970,11 +965,6 @@ def configure_node(o):
 
   o['variables']['node_debug_lib'] = b(options.node_debug_lib)
 
-  if options.debug_http2:
-    o['variables']['debug_http2'] = 1
-  else:
-    o['variables']['debug_http2'] = 'false'
-
   if options.debug_nghttp2:
     o['variables']['debug_nghttp2'] = 1
   else:

node.gypi

@@ -90,10 +90,6 @@
         'NODE_RELEASE_URLBASE="<(node_release_urlbase)"',
       ]
     }],
-    [
-      'debug_http2==1', {
-      'defines': [ 'NODE_DEBUG_HTTP2=1' ]
-    }],
     [ 'v8_enable_i18n_support==1', {
       'defines': [ 'NODE_HAVE_I18N_SUPPORT=1' ],
       'dependencies': [